Reloading 223 / 556 rounds for new ar

A friend of mine just got a new stag ar 15 556 cal. The manual says to only shoot commercially purchased rounds thru it and we are getting into reloading our ammo.....and was going to do reloading and use them for plink shooting. Why the warning....is it ok to shoot our reloads....

JL has it covered, it has nothing to do with the rifle itself, it's all about warranty and legal stuff.
Get a couple of good manuals and learn how to load safe and correctly, you and your rifle will be fine.